Research Interests:
My research interests are centred in the disciplines of geodesy and geodynamics, with an emphasis on ‘environmental geodesy’ – the use of space geodetic tools such as GNSS, satellite altimetry and space gravity applied to global climate change and sea level studies, crustal strain and seismic deformation, and surface expression of hydrologic loading. My PhD work developed an improved in-situ calibration technique for the TOPEX/Poseidon and Jason-1 satellite altimeters. This work continues at the Bass Straight calibration site with the Jason-1 and OSTM/Jason-2 missions as part of our role in the NASA/CNES Ocean Surface Topography Science Team.
More recently my research has focused on error modelling within space geodetic analyses, particularly the influence of different strategies surrounding atmospheric mapping functions, apriori zenith hydrostatic delays, atmospheric loading, and mis-modelling periodic geophysical signals such as the Solid Earth and atmospheric pressure tides. Recent work has also investigated the surface expression of hydrologic loads on the crust, comparing GRACE gravity fields convolved for deformation with observed deformation from GPS analyses. I also have an interest in historical sea level studies and have worked on a novel GPS buoy calibration technique for Australian Antarctic tide gauges, and computed sea level change estimates since Mawson’s 1911-14 AAE expedition to Macquarie Island.
Current work includes collaborative research with the ANU, UNSW and Curtin University as part of a 5 year Australian Research Council Discovery Project: “Environmental Geodesy: Variation in sea level and water storage in the Australian region”. I am also involved in the Calibration, Validation and Retrieval Team (CVRT) on the European Space Agency CryoSat-II mission, working on an Australian contribution to calibration and validation in the East Antarctic.
Interested to study or undertake sabbatical with me in Hobart? Contact me.
Possible Project Topics:
Geodesy related topics that can be tuned to the honours, masters or PhD level are listed below. Undergraduate students are also welcome to come an discuss aspects of these topic areas suitable for the undergraduate level Spatial Research Project unit.
- A space geodetic approach to observing changes in global hydrology
- Error propagation in global GPS analyses: multipath and geometry effects
- Investigating near field effects on Australian CGPS sites
- Systematic errors in space geodesy: using gPhone data to improve the modelling of geophysical signals
- Absolute sea level change: understanding signals in tide gauge and GPS data
- Determination of custral strain using the AuScope CGPS network
- Atmospheric water vapour in Antarctica: A comparison of observed (GPS) vs modelled (ECMWF)
- Structural deformation of the Hobart VLBI telescope
Selected Recent Projects / Publications:
Full Publication List on UTAS WARP Database
2009 - Long GPS coordinate time series: multipath and geometry effects
- Citation: King, M and Watson, C.S., (2009), Long GPS coordinate time series: multipath and geometry effects, Journal of Geophysical Research, Accepted manuscript doi:10.1029/2009JB006543
- Journal URL/PDF: Awaiting pre-production at JGR.
- Synopsis: We investigate the effects of time-variable satellite geometry and the propagation of a time-constant unmodeled multipath signal on long GPS time series. The results highlight the introduction of spurious signals across the frequency domain (including at harmonics of the draconitic year), including very high frequency abrupt changes (offsets) in addition to secular trends. We show that subtle variations in the GPS constellation can propagate multipath signals differently over time, producing significant temporal variations in time series. The propagated signal has noise characteristics that fall between flicker and random walk.
2009 - Atmospheric Effects and Spurious Signals in GPS Analysis
- Citation: Tregoning, P and Watson, C.S., (2009), Atmospheric Effects and Spurious Signals in GPS Analysis, Journal of Geophysical Research, Vol. 114, No. B9, B09403, doi:10.1029/2009JB006344
- Journal URL: JGR Solid Earth, PDF: Here
- Synopsis: This study investigates the influence of different strategies used to handle atmospheric effects in global GPS analyses - specific emphasis is placed on providing quantitative metrics to define solution quality, noise composition and level of spurious signal propogation within various GPS solutions. The VMF1, GMF and NMF mapping functions are investigated, in addition to different methods used to model a priori zenith hydrostatic delay (ZHD) and tidal & nontidal atmopsheric loading.
2009 - Detecting Hydrologic Deformation using GRACE and GPS
- Citation: Tregoning, P., C. Watson, G. Ramillien, H. McQueen, and J. Zhang (2009), Detecting hydrologic deformation using GRACE and GPS, Geophysical Research Letters, 36, L15401, doi:10.1029/2009GL038718.
- Journal URL: Geophysical Research Letters, PDF: Here
- Synopsis: We compute elastic deformation using continental water load estimates derived from the GRACE mission and compare to 3D deformation estimated from GPS data.
The agreement is very good in areas where large hydrologic signals occur over broad spatial scales, with correlation in horizontal components as high as 0.9. Agreement is also observed
at smaller scales, including across Europe. This suggests that: a) both techniques are perhaps more accurate than previously thought and b) a large percentage of the non-linear variations
seen in our GPS time series are most likely related to geophysical processes rather than analysis error.
2008 - Tide Gauge Calibration at Macquarie Island Using GPS buoy techniques
- Citation: Watson, C.S., Coleman, R and Handsworth, R., (2008), Coastal Tide Gauge Calibration: A Case Study at Macquarie Island Using GPS Buoy Techniques, Journal of Coastal Research, 24(4), pgs. 1071-1079.
- Journal URL: Journal of Coastal Research, PDF: Here
- Synopsis: We present results from a novel application of a GPS-equipped buoy to achieve an in situ calibration of a unique inclined tide gauge at Macquarie Island, solving for scale, vertical offset, and sea state–dependent bias parameters. The methodology provides a new, high precision technique using available instrumentation, allowing users to maximise the oceanographic and geodetic value of tide gauge observations.
2008 - Subdaily signals in GPS observations and their effect at semiannual and annual periods
- Citation: King M.A., C.S. Watson, N.T. Penna, P.J. Clarke (2008), Subdaily signals in GPS observations and their effect at semiannual and annual periods, Geophysical Research Letters, 35, L03302, doi:10.1029/2007GL032252.
- Journal URL: Geophysical Research Letters, PDF: Here
- Synopsis: This study investigates residual subdaily signals present within GPS solutions in which site coordinates are parameterised every 5 minutes. These unmodelled signals are shown to propagate into standard 24 h solutions with (among other frequencies) annual and semiannual periods with amplitudes up to 5 mm, with a median amplitude in the height component of 0.8 mm (annual) and 0.6 mm (semiannual).
2007 - Structural Monitoring of Cable-Stayed Bridge: Analysis of GPS versus Modeled Deflections
- Citation: Watson, C.S., Watson, T. and Coleman, R., (2007), Structural Monitoring of Cable-Stayed Bridge: Analysis of GPS versus Modeled Deflections, Journal of Surveying Engineering, 133 (1), pgs. 23-28
- Journal URL: Journal of Surveying Engineering, PDF: Here
- Synopsis: In this study we compare observed GPS deformations observed on a cable-stayed bridge with those determined from a finte element model of the structure. Short term transient motions as well as low frequency thermal deformations were detected and showed high levels of agreement between observed and modelled responses.
2006 - Impact of solid Earth tide models on GPS coordinate and tropospheric time series
- Citation: Watson, C.S., P. Tregoning, and R. Coleman. (2006), Impact of solid Earth tide models on GPS coordinate and tropospheric time series, Geophysical Research Letters, 33, L08306, doi:10.1029/2005GL025538.
- Journal URL: Geophysical Research Letters, PDF: Here
- Synopsis: In this study we present an illustration of how unmodelled sub-daily periodic signals can propagate into time series of daily geodetic coordinates and tropospheric estimates at various different frequencies. We use two solid Earth tide models (IERS2003 and IERS1992) and analyses of global GPS data to quantify proagated signals at annual and semi-annual periods. The spurious signal amplitudes increase as a function of latitude up to approximately 2.0 and 0.4 mm, for the annual and semi-annual case respectively. Tropospheric zenith delay estimates show differences at the 2 mm level, with a dominant diurnal frequency.
2005 - PhD Thesis: Satellite Altimeter Calibration and Validation Using GPS Buoy Technology
- Citation: Watson, C.S., (2005), Satellite Altimeter Calibration and Validation Using GPS Buoy Technology. Available at: http://eprints.utas.edu.au/254/, Thesis for Doctor of Philosophy, Centre for Spatial Information Science, School of Geography and Environmental Studies, University of Tasmania, pgs. 264
- PDF: UTAS eprints
- Synopsis: This work developed an improved in-situ calibration technique for the TOPEX/Poseidon and Jason-1 satellite altimeters. The methodology is based on a purely geometric technique involving the use of GPS equipped buoys and oceanographic moorings. This work continues at the Bass Straight calibration site with the Jason-1 and OSTM/Jason-2 missions as part of our role in the NASA/CNES Ocean Surface Topography Science Team.
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